Garlic Supplementation Reduces Circulating C-reactive Protein, Tumor Necrosis Factor, and Interleukin-6 in Adults: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Background: Conflicting findings on the effects of garlic supplementation on inflammatory biomarkers have been observed in randomized clinical trials (RCTs). Objectives: The aim of this study was to summarize study results regarding the effects of garlic supplementation on serum inflammatory biomarkers in adults. Methods: We searched Scopus, PubMed, Google Scholar and Cochrane library databases for relevant papers published until April 2018, using keywords such as "garlic" and "inflammatory biomarker." We included RCTs that 1) were conducted in adults, 2) examined the effects of garlic supplementation on inflammatory biomarkers compared to a control group, and 3) reported sufficient data on inflammatory biomarkers. Results were reported as weighted mean differences (WMD) with 95% CI using random effects models. Cochrane's Q and I-squared (I-2) tests were used to determine heterogeneity among studies. Funnel plots and Egger's regression test were used to assess publication bias. Results: Sixteen RCTswere included. Garlic doses ranged from 12 to 3600 mg/d, and intervention duration ranged from 2 to 52 wk. Garlic administration significantly reduced serum C-reactive protein (CRP) (n = 13) (WMD: -0.61 mg/L, 95% CI: -1.12, -0.11, P = 0.018, I-2 = 76.9%), IL-6 (n = 5) (WMD: -0.73 ng/L, 95% CI: -1.06, -0.40, P < 0.001, I-2 = 0%), and TNF (n = 7) (WMD: -0.26 ng/L, 95% CI: -0.41, -0.12, P < 0.001, I-2 = 0.0%), compared to controls. However, the effect of garlic supplementation on serum adiponectin (n = 3) (WMD: 0.18 mu g/L, 95% CI: -0.21, 0.57, P = 0.35, I-2 = 60.7%) and leptin (n = 2) (WMD: -1.25 mu g/L, 95% CI: -2.64, 0.14, P = 0.07, I-2 = 0.0%) concentrations were not significant. Conclusion: In this meta-analysis of RCTs, we found that garlic supplementation reduced serum concentrations of CRP, TNF, IL-6, but did not affect serum adiponectin and leptin in adults. More RCTs are needed to test the effects of garlic supplementation on inflammation.